Particles of various types are commonly incorporated into rubber compositions as fillers. For instance, fillers are typically included in the rubber compositions utilized in manufacturing tires, hoses, belts, windshield wiper blades, floor mats, and other rubber products. The fillers are chosen to enhance certain physical characteristics of the rubber composition. Especially in tire art, the use of carbon black, silica, and crosslinked polymers as fillers is well known. The addition of fillers tends to improve the physical properties of the polymer matrices to which they are added. For instance, the inclusion of carbon black and silica in tire tread rubber compounds is critical to attain required strength and tread wear characteristics. However, such tires have the disadvantage that they have a high rolling resistance, which is related to hysteresis loss. With the increasing demand for automobile safety and low fuel consumption, the specifications for tire tread elastomeric compounds have become more critical. Tire treads are expected to have high abrasion resistance in order to provide a long life expectancy, to exhibit good anti-skid properties in both wet and dry conditions, and to have low hysteresis characteristics at elevated temperatures in order to provide low rolling resistance and reduced dynamic heat build-up. Therefore, numerous attempts have been made in the design of both elastomer matrices and fillers.
U.S. Pat. No. 5,395,891 and U.S. Pat. No. 6,127,488 to Obrecht disclose the use of crosslinked polybutadiene and crosslinked styrene-butadiene copolymers, respectively, as fillers. The purported benefit of the inclusion of these crosslinked rubber particles in rubber formulations is lower hysteresis. Additionally, polybutadiene gels have been shown to impart improved abrasion resistance while styrene-butadiene copolymer gels have demonstrated improved wet traction characteristics. U.S. Pat. No. 6,133,364, U.S. Pat. No. 6,207,757, and U.S. Pat. No. 6,242,534 to Obrecht et al disclose a rubber composition comprising a crosslinked elastomer particle and a non-crosslinked elastomer. The crosslinked elastomeric particles are functionalized to impart unique surface reactivity for improved coupling with the non-crosslinked host elastomer as well as the subsequent ability to employ coupling agents other than the conventional sulfur-bridged bis-alkoxy silanes. The benefits of these gels in tire tread compositions are reported to be lower hysteresis, improved abrasion resistance, and improved wet traction. However, using these gel particles as fillers shows some critical drawbacks such as inferior mechanical properties (e.g. 300% moduli, tear and abrasion resistance). U.S. Pat. No. 6,620,866 discloses a rubber mixture containing agglomerated rubber gels. The purpose of using the high-pressure agglomerated gels is to improve the recognized deficiency in the mechanical properties.
U.S. Pat. No. 6,747,095 and U.S. Pat. No. 6,653,404 to Konno et al disclose a rubber composition comprising as essential components a crosslinked polymer particle and a non-crosslinked rubber component. The rubber composition may be used to obtain a vulcanized rubber. The crosslinked polymer particles are intended for use as filler to provide a rubber composition having good processability and handling performance as well as improved tensile strength and wear resistance when vulcanized.